1. Field of the Invention
The present invention relates generally to wireless communication systems and, more particularly, to mobile station receiver architectures and methods that employ detection and synchronization techniques.
2. Description of Related Art
A conventional wireless communication system may comprise elements such as a client terminal or mobile station (“MS”) and multiple base stations (“BS”). FIG. 1 presents a wireless cellular communication system 10, which comprises elements such as MS 12 and BSs 14. Other network devices which may be employed, such as a mobile switching center, are not shown. The communication path from a given BS 14 such as the “serving base station” to the MS 12 is referred to herein as the downlink (“DL”) and the communication path from the MS 12 to a base station 14 is referred to herein as the uplink (“UL”).
As shown in FIG. 2, the MS 12 typically includes a baseband subsystem and a radio frequency (“RF”) subsystem. Memory, such as an external memory 20, is shown connected to the baseband subsystem. The baseband subsystem normally consists of a micro controller unit (“MCU”), a signal processing unit (“SPU”), data converters, peripherals, power management, and memory as shown in FIG. 3. The SPU may be a digital signal processor (“DSP”), hardware (“HW”) accelerators, co-processors or a combination of the above. Normally the overall control of the baseband subsystem is performed by software running on the MCU and the processing of signals is done by the SPU.
The radio frequency spectrum is the precious resource and it is limited. Conventional wireless communication systems may operate in different radio frequency bands for different markets. Normally, for a given wireless communication system, the radio frequency band is divided into multiple channels. To meet the requirements of different markets and to efficiently use the limited radio frequency spectrum, many deployed wireless communication systems are designed to allow the scalability and flexibility of operating it in different frequency bands using different channel bandwidths.
The combination of frequency band of operation, channel bandwidth, and other parameters is collectively referred as a radio profile of the wireless communication network. A wireless communication network may have multiple radio profiles. To support this flexibility in wireless communication networks, MSs should be able to dynamically detect radio profiles available for service.
A wireless communication system may be deployed in one geographic area with one radio profile while the same system may be deployed in different geographic area with different radio profile. The MSs in these systems do not have a priori knowledge about the actual radio profile being used by the system. An MS in these systems needs to determine the actual radio profile being used by the system. The determination of radio profile typically needs to be done under different circumstances.
In order to understand some of the issues and tradeoffs involved, an example is now provided for a wireless communication system in accordance with the IEEE 802.16e standard. This standard includes an Orthogonal Frequency Division Multiple Access (“OFDMA”) based physical layer, which can use any of the radio profiles listed in the table of FIG. 4. A number of different radio profiles are shown, with each given an RF profile name. The channel bandwidth, Fast Fourier Transform (“FFT”) size, center frequency step, start frequency (Fstart) and range or number of channel positions (Nrange) are also listed. While additional profiles may be added, important attributes of the radio profiles of IEEE 802.16e system are the frequency band of operation, the channel bandwidth being used and the FFT size being used. FFT is used interchangeably herein with FFT size.
Normally detecting the radio profile involves several steps. First, the frequency band of operation is identified. This typically can be determined by signal level measurements in all frequency bands supported by the wireless communication system and the client terminal. The next step of the radio profile detection involves finding the exact location of the channel within a frequency band for a given bandwidth. Note that for each profile, there are hundreds of channel positions as shown in FIG. 4. The fine resolution in channel position for a given frequency band allows deployment flexibility. For example, the profile Prof1.A—2.3 in FIG. 4 contains a total of 365 (0, . . . , 364) channel positions even though there may be at most 10 actual channels that can be deployed in that frequency band. The MS considers all the positions when detecting the radio profile in a worst case scenario.
The process of detecting the radio profile in known systems is implemented in an exhaustive manner where every possible combination is tried sequentially until the radio profile used by the wireless communication networks are detected successfully. For the chosen example, assuming the frequency band of operation is identified as 2.3 GHz, the possible radio profiles are numbers 1 through 5 in FIG. 4. For this frequency band there are four possible channel bandwidths (3.5 MHz, 5.0 MHz, 8.75 MHz and 10.0 MHz) and two different FFT sizes (512 and 1024).
For each channel position the MS or client terminal must detect the correct channel bandwidth and FFT pair. In one possible implementation of radio profile detection, a client terminal may first attempt to detect radio profile 1 using 8.75 MHz channel bandwidth with 1024 FFT and may need to search for all 365 channel positions. If the radio profile detection is not successful, the client terminal may attempt to detect a radio profile 2 using 5 MHz channel bandwidth with 512 FFT and may need to search for all channel positions and this process continues for all radio profiles 1 through 5 for that frequency band.
In another possible implementation of radio profile detection, a client terminal may first attempt to detect a radio profile for a given channel position. In this case for a given channel position all the allowed channel bandwidth and the FFT pair is searched for. The possible channel bandwidth and the FFT pair are 8.75 MHz channel bandwidth with 1024 FFT pair or 5 MHz channel bandwidth with 512 FFT pair or 10 MHz channel bandwidth with 1024 FFT pair or 3.5 MHz channel bandwidth with 512 FFT pair. If the radio profile detection is not successful for the channel position, the client terminal may attempt to detect the radio profile for the next channel position. As these scenarios illustrate, the process of detecting the radio profile becomes much more processing intensive due to large number of possible combinations.
It should be understood that the exhaustive approach for radio profile detection has several major disadvantages. For instance, it may take a long time to detect the radio profile. And such detection may consume significant power in the MS as the processing is intensive.
Furthermore, a radio profile may need to be detected at different scenarios. These include when the client terminal powers on, when the client terminal is looking for network service, when the client terminal roaming to a new service area, etc. Often the client terminals for IEEE 802.16e are battery operated devices. Thus, another issue of concern is power consumption by such devices.